GrayCode.java

Below is the syntax highlighted version of GrayCode.java from §2.3 Recursion.

/******************************************************************************
 *  Compilation:  javac GrayCode.java
 *  Execution:    java GrayCode n
 *
 *  Print the n-bit binary reflected Gray code using recursion.
 *
 *  % java GrayCode 3
 *  000
 *  001
 *  011
 *  010
 *  110
 *  111
 *  101
 *  100
 *
 ******************************************************************************/

public class GrayCode {

    // append reverse of order n gray code to prefix string, and print
    public static void yarg(String prefix, int n) {
        if (n == 0) StdOut.println(prefix);
        else {
            gray(prefix + "1", n - 1);
            yarg(prefix + "0", n - 1);
        }
    }

    // append order n gray code to end of prefix string, and print
    public static void gray(String prefix, int n) {
        if (n == 0) StdOut.println(prefix);
        else {
            gray(prefix + "0", n - 1);
            yarg(prefix + "1", n - 1);
        }
    }


    public static void main(String[] args) {
        int n = Integer.parseInt(args[0]);
        gray("", n);
    }

}